Rhythmic Growth-Induced Concentric Ring-Banded Structures in Poly(ε-caprolactone) Solution-Casting Films Obtained at the Slow Solvent Evaporation Rate

Wang, Zongbao; Hu, Zhijun; Chen, Yongzhong; Gong, Yumei; Huang, Haiying; He, Tianbai

doi:10.1021/ma070334+

Cited by 68 publications

(90 citation statements)

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“…The surface height fluctuation of the two types of birefringent polymer banded spherulite is in the order of tens of nanometers, less than 1% of the film thickness. In contrast, in the nonbirefringent banded spherulites formed from all flat-on lamellar crystals, the height fluctuation is up to the whole thickness of the sample [1][2][3].…”

Section: Organization Of Twisted Lamellae In Banded Spherulitesmentioning

confidence: 89%

“…In the former case, the bands are due to the periodical modulation of sample thickness and there is no variation of refractive index in the spherulite. These nonbirefringent banded spherulites have been observed in some polymer single crystals formed from thin melt films [1] or solutions [2] and are reviewed by Li et al [3] in this special issue. In the latter case, the birefringent bands can result from the wavy bending growth or twisting growth of crystals.…”

Section: Introductionmentioning

confidence: 99%

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Organization of Twisting Lamellar Crystals in Birefringent Banded Polymer Spherulites: A Mini-Review

Zhang

et al. 2017

Crystals

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Abstract:In this mini-review, we summarize the evidences of lamellar twisting in the birefringent banded polymer spherulites demonstrated by various characterization techniques, such as polarized optical microscopy, real-time atomic force microscopy, micro-focus wide angle X-ray diffraction, etc. The real-time observation of lamellar growth under atomic force microscopy unveiled the fine details of lamellar twisting and branching in the banded spherulites of poly(R-3-hydroxybutyrate-co-17 mol % R-3-hydroxyhexanoate). Organization of the twisting lamellar crystals in the banded spherulites was revealed as well. The lamellar crystals change the orientation via twisting rather than the macro screw dislocations. In fact, macro screw dislocation provides the mechanism of synchronous twisting of neighboring lamellar crystals. The driving force of lamellar twisting is attributed to the anisotropic and unbalanced surface stresses. Besides molecular chirality, variation of the growth axis and the chemical groups on lamellar surface can change the distribution of the surface stresses, and thus may invert the handedness of lamellar twisting. Thus, based on both experimental results and physical reasoning, the relation between crystal chirality and chemical molecular structures has been suggested, via the bridge of the distribution of surface stresses. The factors affecting band spacing are briefly discussed. Some remaining questions and the perspective of the topic are highlighted.Keywords: banded polymer spherulite; ringed spherulite; lamellar twisting; organization of lamellar crystals; surface stresses; chirality When crystallized from quiescent melt or concentrated solution, polymer chains usually form spherulites consisted of multiple lamellar crystals radiating from the spherulite center. Observed under polarized optical microscope (POM), a spherulite shows the characteristic Maltese-cross extinction. Besides the Maltese cross, some spherulites demonstrate alternative bright and dark bands under POM. These spherulites are termed as banded spherulites or ringed spherulites. The band structure with different light intensities may result from different thicknesses or different birefringences but similar thickness. In the former case, the bands are due to the periodical modulation of sample thickness and there is no variation of refractive index in the spherulite. These nonbirefringent banded spherulites have been observed in some polymer single crystals formed from thin melt films [1] or solutions [2] and are reviewed by Li et al. [3] in this special issue. In the latter case, the birefringent bands can result from the wavy bending growth or twisting growth of crystals. The wavy bands have been reported in sheared liquid crystals [4,5], which do not form spherulites under the condition. In this mini-review, we focus on the birefringent banded spherulites, which consist of synchronously twisted lamellar crystals. The organization of the twisted lamellar crystals in the banded spherulites and the driving force for lamell...

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Section: Organization Of Twisted Lamellae In Banded Spherulitesmentioning

confidence: 89%

Section: Introductionmentioning

confidence: 99%

Organization of Twisting Lamellar Crystals in Birefringent Banded Polymer Spherulites: A Mini-Review

Zhang

et al. 2017

Crystals

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“…1.50 × 10 −4 mL·h −1 at 20 • C [44,45]. Both the non-birefringent and birefringent concentric ringed morphologies, as exhibited in Figure 4, were observed by changing the initial concentration of the casting solution.…”

Section: Manipulating the Stacking Of Radial Lamellae To Prepare Concmentioning

confidence: 95%

“…It is obvious that the birefringent property depends on the initial solution concentration, for which determines the thickness of the resultant films. The lower initial solution concentration leads to the thinner film, in which the spherulites are composed of almost uniform flat-on lamellae because of the combination of a strong polymer-substrate interplay and the slow spherulite radial growth, so a non-birefringent pattern is observable in the uniaxial PCL spherulites with the radial and tangential directions along the fixed crystallographic b-and a-axis, respectively (Figure 5a) [44]. As the films thicken with increasing initial solution concentration, the lamellae orientations change from the uniform flat-on case near the substrate to become gradually tilted and, eventually, edge-on situations toward the top layers of the ridges (Figure 5b) [45].…”

Section: Manipulating the Stacking Of Radial Lamellae To Prepare Concmentioning

confidence: 99%

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Morphological Control of Polymer Spherulites via Manipulating Radial Lamellar Organization upon Evaporative Crystallization: A Mini Review

Wang

2017

Crystals

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Abstract:Various spherulites or spherulitic crystals are widely encountered in polymeric materials when crystallized from viscous melts or concentrated solutions. However, the microstructures and growth processes are quite complicated and remain unclear and, thus, the formation mechanisms are rather elusive. Here, diverse kinds of spherulitic growths and patterns of typical polyesters via evaporative crystallization of solution-cast thin films are delineated after detailed investigating the microstructures and in situ following the developing processes. The spherulitic crystals produced under different evaporation conditions reflect variously optical features, such as the usual Maltese Cross, non-birefringent or half-birefringent concentric-rings, extinction spiral banding, and even a nested ring-banded pattern. Polymer spherulites are composed of stacks of radial fibrillar lamellae, and the diversity of bewitchingly spherulitic morphologies is dominated by the arrangement and organization of radial lamellae, which is predicted to be tunable by modulating the evaporative crystallization processes. The emergence of various types of spherulitic morphologies of the same polymer is attributed to a precise manipulation of the radial lamellar organization by a coupling of structural features and specific crystal evolving courses under confined evaporation environments. The present findings improve dramatically the understanding of the structural development and crystallization mechanism for emergence of diverse polymer spherulitic morphologies.

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Unconventional Non‐birefringent or Birefringent Concentric Ring‐Banded Spherulites in Poly(L‐lactic acid) Thin Films

Nurkhamidah

Woo

2013

Macro Chemistry & Physics

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Unconventional concentric up-and-down bands, differing from the conventional brightextinction or blue/orange bands in other polymers, in poly( L -lactic acid) are found via controlled thin fi lms. Non-birefringent and birefringent concentric banded spherulites are obtained from 350-400 nm and 1800-2000 nm fi lm thicknesses, respectively. Non-birefringent concentric ring-banded spherulites are arranged only by fl at-on lamellae; in contrast, complex combinations of fl at-on, edge-on, and round-shaped lamellae in four transitional zones are present within a single band in the thicker fi lms of birefringent, concentric, ring-banded spherulites. Interband is an optically extinction crevice that segregates two neighboring bands. Unique lamellar arrangements at specifi c T c and thickness confi nement are two factors for the unconventional concentric bands.

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Rhythmic Growth-Induced Concentric Ring-Banded Structures in Poly(ε-caprolactone) Solution-Casting Films Obtained at the Slow Solvent Evaporation Rate

Cited by 68 publications

References 35 publications

Organization of Twisting Lamellar Crystals in Birefringent Banded Polymer Spherulites: A Mini-Review

Organization of Twisting Lamellar Crystals in Birefringent Banded Polymer Spherulites: A Mini-Review

Morphological Control of Polymer Spherulites via Manipulating Radial Lamellar Organization upon Evaporative Crystallization: A Mini Review

Unconventional Non‐birefringent or Birefringent Concentric Ring‐Banded Spherulites in Poly(L‐lactic acid) Thin Films

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